linux-kernel - Re: [PATCH v3 5/5] KVM: SVM: Enable shadow stack virtualization for SVM

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Message-ID: <aKu9VfW0FF5YeABi@intel.com>
Date: Mon, 25 Aug 2025 09:33:09 +0800
From: Chao Gao <chao.gao@...el.com>
To: John Allen <john.allen@....com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<seanjc@...gle.com>, <pbonzini@...hat.com>, <dave.hansen@...el.com>,
	<rick.p.edgecombe@...el.com>, <mlevitsk@...hat.com>,
	<weijiang.yang@...el.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<hpa@...or.com>, <mingo@...hat.com>, <tglx@...utronix.de>,
	<thomas.lendacky@....com>
Subject: Re: [PATCH v3 5/5] KVM: SVM: Enable shadow stack virtualization for
 SVM

On Wed, Aug 06, 2025 at 08:45:10PM +0000, John Allen wrote:
>Remove the explicit clearing of shadow stack CPU capabilities.
>
>Signed-off-by: John Allen <john.allen@....com>
>---
>v3:
>  - New in v3.
>---
> arch/x86/kvm/svm/svm.c | 5 -----
> 1 file changed, 5 deletions(-)
>
>diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>index 82cde3578c96..b67aa546d8f4 100644
>--- a/arch/x86/kvm/svm/svm.c
>+++ b/arch/x86/kvm/svm/svm.c
>@@ -5255,11 +5255,6 @@ static __init void svm_set_cpu_caps(void)
> 	kvm_set_cpu_caps();
> 
> 	kvm_caps.supported_perf_cap = 0;
>-	kvm_caps.supported_xss = 0;
>-
>-	/* KVM doesn't yet support CET virtualization for SVM. */
>-	kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
>-	kvm_cpu_cap_clear(X86_FEATURE_IBT);

IIUC, IBT should be cleared because KVM doesn't support IBT for SVM.

With this fixed:

Reviewed-by: Chao Gao <chao.gao@...el.com>

> 
> 	/* CPUID 0x80000001 and 0x8000000A (SVM features) */
> 	if (nested) {
>-- 
>2.34.1
>